This invention provides an improved method and apparatus for making blown plastic containers which have a hollow handle on one side with the handle of one-piece construction with the body of the container. The container is formed on an injection molding machine with a special pre-blow mold having a cavity into which a part of a parison is displaced to form a handle portion of the partially blown container. This handle portion which is hollow and curved along its outer edge region to the shape of the final handle, is then collapsed or compressed over a portion of its area.
The compressed area comprises the area between the body of the partially blown container and the outer part of the handle portion which will constitute a hollow bail handle of the final product. The compressed part of the handle portion is sheared from the remainder of the partially blown container and this shearing operation is performed while the molten material of the parison is still hot enough to seal over the lines where the compressed plastic is separated from the hollow portions of the partially blown container. These hollow portions are the handle along its entire length and the body portion to which the handle connects.
The blowing mold in which the parison is initially blown to form the partially blown container is of special construction. It has a plunger, shaped to the area which is to be compressed, and has a complementary support on the opposite side of the area that is to be compressed. The plunger and the support are both movable so as to apply force to opposite sides of the area of the handle portion which is to be compressed between them. After compressing the plastic between the plunger and the support so as to make it no longer hollow, the plunger and support are then moved in such a way as to shear the compressed area from the remainder of the handle portion, which is still hollow, and from the side of the partially blown container.
The sheared material is moved downward in the die and the apparatus has means for stripping the sheared material from the support so that it can be discharged to a waste receptacle and leave the support clear for operation on a second partially blown container.
The plunger and the support form portions of the wall of the cavity space into which plastic is displaced to make the handle portion.
Another feature used in the preferred embodiment of the invention is the stretching of the parison for a substantial distance lengthwise of the core rod on which the parison is formed. This stretching is preferably done after an initial blowing or the parison to free it from friction against the core rod and the stretching is preferably formed by the pressure of the blowing fluid that is introduced into the parison.
The blow mold in which the container is partially blown is preferably made with a diameter only slightly greater than the diameter of the original parison so that the initial blowing in the first blow mold does not expand the diameter or the circumference to any great degree but does the consequential stretching of the plastic for axial orientation in a lengthwise direction where the cavity of the mold is substantially longer than the parison.
In order to prevent sagging of the extended end of the parison, while in the first blow mold and during transfer from the first blow mold to a second blow mold, the preferred embodiment of the invention has a core rod with an end portion which telescopes into the main portion of the core rod. During stretching of the parison, the end of the core rod, which is telescoped into the main portion, is extended to a length approaching that of the partially blown parison so as to provide a support, if necessary, for the end of the parison which is beyond the original end of the core rod.
In the preferred embodiment, the partially formed container and its hollow handle are transferred to a second blow mold with a cavity shaped to the final coutour of the container and in a subsequent blowing step, in this second blow mold, the partially blown container and handle are expanded to their final shape and size.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.